(1) Field of the Invention
The invention relates to a device for controlling the variation of the power and/or the speed of a load, for example, such as an asynchronous, a synchronous, or a universal motor, a transformer, an inductor, a condenser, or a resistor, comprising a switch connected to a phase of a single-phase or multiphase alternating-current supply-circuit, this switch being associated with means for controlling the cyclic ratio .alpha./T, in which .alpha. corresponds to the time of opening or closing of the circuit by the switch, and T is the period of the phase on which this latter is placed.
(2) Description of the Prior Art
As a device for controlling the variation of the power and/or the speed of a load, such as, for example, an asynchronous, a synchronous, or a universal motor, a transformer, an inductance, a condenser or a resistor, for the time being there is more particularly known the triac regulator and the high-frequency chopper grouping, as described above, a switch placed on the alternating-current supply-circuit as well as means for controlling the time of opening and/or closing of this circuit by the switch during an alternation or period of the supply circuit. These control means thus modulate the speed and/or the power of the load.
However, these known control devices have a number of drawbacks.
For example, the triac regulator has an unflexible operation and, when switching, generates very high current-peaks in the supply network which it is connected to. This results in the generation of noises in the magnetic circuits and in the supply of harmonic currents to the load, generating high counter electromotive forces and a very low torque at low speed. Such a device creates radio- and television interferences and harmonics which contaminate the supply network.
The control device of the high-frequency chopper type copes with the drawback of the magnetic noise generated by the triac regulator by transferring this noise to frequencies that are inaudible to the human ear. However, such a control device causes the transistors it is comprised of, as well as the load, to overheat. This overheating of the transistors results from the numerous switchings generated by this chopper, while the overheating of the load is due to losses from Foucault (eddy) currents in the magnetic circuits. In addition, with such a high-frequency chopper, the same drawbacks as those already mentioned with respect to the triac regulator, such as generation of counter electromotive forces by the load, radio- and television interferences and harmonics contaminating the network, are experienced.